Self-monitoring of blood glucose (SMBG) is important for diabetic patients to manage their blood glucose levels and to use this monitoring in treatment. Simple blood glucose self-monitoring devices using an electrochemical biosensor have recently been widely used in SMBG. The biosensor includes an insulating substrate on which electrodes and an enzyme reaction layer are formed.
Examples of enzymes used herein include glucose dehydrogenase (GDH), glucose oxidase (GO), and the like. In terms of methods using GO (EC 1.1.3.4), a problem has been noted in that dissolved oxygen in a measurement sample is likely to affect the measurement results. Although GDH is unaffected by dissolved oxygen, it is not suitable for accurately measuring blood glucose levels, because, for example, a pyrroloquinoline quinone-dependent glucose dehydrogenase (PQQ-GDH) (EC 1.1.5.2 (formerly EC 1.1.99.17)) acts on sugars such as maltose and lactose, in addition to glucose.
A flavin adenine dinucleotide-dependent glucose dehydrogenase (hereinafter also referred to as “FADGDH”) is known to be unaffected by dissolved oxygen and to have almost no action on maltose.
For example, Patent Documents 1 to 5 report enzymes derived from Aspergillus terreus and Aspergillus oryzae, and modifications of these.
Non-patent Document 1 reports an enzyme derived from Glomerella cingulata, which is ascomycete (asexual stage name: Colletotricum gloeosporoides).
These enzymes, however, have relatively high reactivity to xylose (Patent Document 1 and Non-patent Document 1), and there is therefore room for improvement in accurately measuring blood glucose of people who are undergoing a xylose tolerance test.
Further, a flavin-bound GDH having relatively low action on xylose (Patent Document 6), a modified GDH having combined advantages of GO and GDH (Patent Document 7), and the like, have recently been developed, but there is still room for improvement.